The goal here is to offload aux retries handling from the
drivers to drm.
However there are 2 differents cases for retry:
1. Immediately retry - Hardware already took care of needed timeouts
before answering that a retry is possible.
2. Busy - Wait some time and retry.
This driver introduce the support for EAGAIN that can handle the
first case and a following patch will introduce EBUSY waits,
after all drivers counting on immediately retries are changed.
v2: Rebased on top of drm_dp_helper docbook changes.
Also this version add EAGAIN documentation and as suggested by
Jani it inserts a comment at drm_dp_i2c_do_msg explaining EAGAIN
timeout is already handled at i2c level.
Cc: Jani Nikula <jani.nik...@intel.com>
Cc: Dave Airlie <airl...@redhat.com>
Signed-off-by: Rodrigo Vivi <rodrigo.v...@intel.com>
Tested-by: Daniel Stone <dani...@collabora.com>
Signed-off-by: Rodrigo Vivi <rodrigo.v...@intel.com>
---
drivers/gpu/drm/drm_dp_helper.c | 10 ++++++++++
include/drm/drm_dp_helper.h | 4 ++++
2 files changed, 14 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 9535c5b..2e26097 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -198,6 +198,11 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8
request,
err = aux->transfer(aux, &msg);
mutex_unlock(&aux->hw_mutex);
if (err < 0) {
+ /* Immediately retry */
+ if (err == -EAGAIN)
+ continue;
+
+ /* FIXME: On BUSY we could wait before retrying */
if (err == -EBUSY)
continue;
@@ -547,6 +552,11 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux,
struct drm_dp_aux_msg *msg)
ret = aux->transfer(aux, msg);
mutex_unlock(&aux->hw_mutex);
if (ret < 0) {
+
+ /*
+ * -EAGAIN retries are handled by i2c layer with
+ * timeouts for repeated -EAGAINs
+ */
if (ret == -EBUSY)
continue;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index ed7dbdc..518fc1b 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -758,6 +758,10 @@ struct drm_dp_aux {
* to check for failure.
* - -EBUSY: When BUSY helpers will attempt retries before propagating
* this error.
+ * - -EAGAIN: DPCD helper will attempt immediatelly retries before
+ * propagating this error. i2c helper will only propagate directly
+ * since i2c layer already perform retries with timeouts for repeated
+ * -EAGAINs.
*
* Note that the aux helper code assumes that the .transfer() function
* only modifies the reply field of the drm_dp_aux_msg structure. The
--
2.4.3
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